Purified Chloroform. Chloroformum Purificatum

Chloroformum Purifica-tum. U. S. - Chloroformum. Br., U. S. 1850.

Discovery. Chloroform was discovered, in the year 1831, by Mr. Samuel Guthrie, of Sackett's Harbour, New York, and about the same time by Soubeiran in France, and Liebig in Germany; but the precise chemical nature of the product was not understood, till determined by Dumas in 1834. By that chemist it was ascertained to be a compound of three eqs. of chlorine with one eq. of a bicarburet of hydrogen called formyle, or, in other words, to be a terchloride of formyle. Mr. Guthrie, mistakingly supposing that the substance obtained by him was the Dutch liquid, or chloric ether of Dr. T. Thomson, gave it the latter name, which is still, though very erroneously, sometimes applied to its alcoholic solution.

Preparation

The chloroform of commerce is prepared on a large scale by the chemical manufacturer. The process consists in distilling a mixture of chlorinated lime (chloride of lime), water, and alcohol. Two liquids are condensed in the receiver, the heavier of which is chloroform. This, having been separated, is purified by washing with water, and by other processes differing somewhat with different manufacturers; but, in the crude state in which it is delivered to commerce, though fitted for external use and for various pharmaceutical purposes, it is often insufficiently pure for inhalation. The U. S. Pharmacopoeia, therefore, very properly gives a process for its purification, and designates the product as Purified Chloroform.

Purified Chloroform. Chloroformum Purificatum. U. S. The process of purification consists in first mixing and occasionally shaking together for twenty-four hours commercial chloroform and sulphuric acid, then separating the lighter supernatant liquid, mixing it with a little stronger alcohol, adding carbonate of potassa previously heated to redness, and finally, after agitating the mixture thoroughly, distilling by means of a water-bath to dryness. The reaction by which the chloroform is produced takes place between the alcohol and the chlorine of the chlorinated lime; but along with the proper chloroform, other products are generated, among which is a chlorinated pyrogenous oil, which comes over with the chloroform. Some alcohol also distils over, and probably chlorine liberated by the reactions which take place. These are separated by washing with water. In the U. S. process of purification, the sulphuric acid is added in order to remove the pyrogenous oil, which it decomposes and destroys; and a little stronger alcohol and carbonate of potassa are subsequently added, to separate water and any sulphurous acid that may result from the partial decomposition of the sulphuric acid.

Properties

Chloroform is a limpid, colourless liquid, of a fragrant, ethereal, apple-like odour, and a warm, sweet, somewhat pungent, and agreeable taste. it rapidly volatilizes on exposure, and boils at 142° P. it is not inflammable. its specific gravity is 1 49. When thrown into water it sinks rapidly, forming as it falls distinct globules, which have a characteristic appearance. it is very slightly soluble in water, requiring for solution 2000 parts of that liquid, to which nevertheless it distinctly imparts its peculiar odour. Alcohol and ether readily dissolve it; and its alcoholic solution, if not containing more than about ten per cent. of chloroform, mixes with water without being decomposed, and forms a liquid of a sweet, aromatic, and grateful taste. it has itself extraordinary solvent powers; dissolving not only most of the substances soluble in alcohol, such as the volatile oils, resins, camphor, etc., but also some which are not so, or but imperfectly, as gutta percha, caoutchouc, and wax. The cohesion between its particles must be feeble, as it yields a greater number of drops from a certain measure than any other medicinal liquid; one fluidrachm giving on an average 240 drops.* its sensible properties, great specific gravity, behaviour with water, volatility without residue, low boiling point, and incombustibility, sufficiently distinguish it from all other bodies, +

* in reference to this point, Prof. Procter, at my request, made numerous trials with bottles of differently-shaped mouths, such as are usually employed for holding medicines. The highest number of drops yielded by a fluidrachm of pure chloroform was 255, and the lowest 230. From a glass phial with a recurved lip, which always yields unusually large drops, he obtained 160 to the fluidrachm.

+ The following mode of detecting chloroform in the blood has been proposed. When heated to redness, its vapour is decomposed, yielding with other products chlorine and hydrochloric acid. if a liquid containing a little chloroform be placed in a Florence flask, provided with a cork fitted into its neck, through which passes a tube of hard glass, twelve or fifteen inches long, and if the flask be now heated to 160° so as to vaporize the chloroform, and the middle part of the tube heated to redness by means of a spirit lamp, the vapour escaping through the outer end of the tube will be found to redden litmus-paper, to render blue starch paper previously wetted with solution of iodide of potassium, and to precipitate white a solution of nitrate of silver, thus indicating the presence of the two products of decomposition referred to. This experiment has been tried with a quantity of putrid blood, containing two drops of chloroform, and proved perfectly successful. The test, however, does not seem to have answered practically; for in one fatal case, and in three cases in which the system was fully under the influence of chloroform, not a particle could be detected. The inference is that, if in the blood at all, it was in a proportion too small to yield evidence of its presence. (Guy's Hospit. Rep., x. 200, a.d. 1864.) Nevertheless, negative results of this kind must be more largely accu mulated before they can be considered as conclusive; and in any doubtful case of chloroform poisoning, it would be proper to apply the test, as its evidence if positive would decide the question. (Note to the third edition.) day he could remember nothing of what had passed, and the unpleasant symptoms gradually disappeared. (Bull, de Thérap., xlii. 296.)